It is proposed to study the projections of corticospinal pathways into spinal motoneurons in normal man and in subjects with "cerebral palsy". Two technical developments make this project feasible. 1. It is possible to activate corticospinal pathways in awake man using a brief magnetic field. Considerable attention has been given to the possible side effects of such stimulation (see details in body of application). No harmful effects have been reported. 2. The applicant has developed a method for deriving information about post synaptic potentials in single human motoneurons from changing in firing probability of voluntarily activated motor units. The relationship between the shape of a PSP and the profile of the changes in firing probability that it produces is complex but is now well understood. Thus it is possible to derive the projection frequency of a given fiber system onto a pool of motoneurons and estimate the rise times and relative magnitudes of the PSPs. The principal project for the next research period will be to document the short latency projections of corticospinal pathways activated by magnetic stimulation in normal subjects. We will then test the hypothesis that the projections are altered by lesions of the nervous system which occur when these pathways are developing. Our preliminary studies on patients with "cerebral palsy" indicate that these projections are grossly deranged and that subgroups of the cerebral palsy can be identified on the basis. Thus this study promises to be highly rewarding.